The Great Wall has three major components: passes, signal towers (beacons), and walls. The design of each of these features has been determined by strategic importance.

Passes

 

As major strongholds along the wall, passes usually are located at key positions such as intersections with trade routes.

 

Situated at key positions, usually on trade routes, passes were needed to allow controlled entry to and exit from Chinese territory. A straight forward gate would be vulnerable to attack and for this reason complex constructions were necessary. These could vary from a simple double wall to a virtual castle with a maze like format to enable the defending forces to control any attempt at an invasion. An important consideration in design was that the fortifications should always be such that a small number of defenders should have the ability to repel a much larger attacking force.

The ramparts were reinforced with huge bricks and stones with earth and crushed rock as a filler. Great bastions that measured some 10 meters (30 feet) in height and up to 5 meters in width at the top enhanced the protection afforded by the wall. Access to the top of the wall for both horses and men was provided by ramps and ladders within the pass. Outer parapets were battlemented to give cover for archers and a low wall approximately 1 meter high ran along the inner side for the safety of both men and horses.

There were occasions when it was necessary for troops to go out into the countryside beyond the wall and it was the gate within the passes that gave them access to the outside whether is was to mount a counter attack or merely go on patrol.

The gate would be protected by enormous double timber doors secured with huge iron bolts and locking rings. Above each gate there was a tower. Typically these would be two or three storeys high to give the garrison the advantage of a lookout from which it was possible to see the approach of travellers or marauders who could be a threat. These towers were of timber or brick or both. What was known as a weng-cheng, a semicircular or polygonal construction was built outside the gate to provide cover against direct attack. At certain of the more important and therefore more vulnerable gates an additional fortification called a luo-cheng was constructed. This would have the benefit of a tower upon it and so could act as an additional lookout or post from which troops could be directed during any hostilities. The ditches formed by the excavation of soil to fill the walls would be extended to create a protective moat around the entrance to the gate providing a further device to slow down the progress of invaders and thereby giving the defending forces a greater opportunity to repel them.